SOME months ago (vol. vii. p. 443) I sent you an extract from a letter from Mr. Hague, a geologist residing in California, who gave me a very curious account of the terrifying effect on the other ants of the sight of a few which he had killed on one of their paths.1 Mr. Traherne Moggridge2 saw this account in NATURE, and wrote to me that he had heard from a gentleman who had lived in Australia that merely drawing a finger across the path deters ants from crossing the line.

Mr. Moggridge tried this experiment with some ants at Mentone with similar effects. I therefore sent the letter to Mr. Hague, and asked him to observe whether his ants were alarmed by the smell left by the finger, or were really terrified by the sight of their dead and dying comrades. The case appears curious, as I believe no one has ever observed an invertebrate animal realising danger by seeing the corpses of a fellow species. It is indeed very doubtful whether the higher animals can draw any such inferences from the sight; but I believe that everyone who has had experience in trapping animals is convinced that individuals who have never been caught learn that a trap is dangerous by seeing others caught.

"By a somewhat singular coincidence the first reappearance, since last winter, of any ants in the room where I then observed them occurred on the day when your last note arrived,—that is, after an interval of several months. Then a few were observed about the tumbler at the middle of the shelf and the vase at the other end from that whence they were first driven, although they all came from a hole near the base of the mantel, directly beneath the vase which they avoided.

"Acting on Mr. M's. suggestion, I first tried making simple finger marks on their path (the mantel is of marble) and found just the results which he describes in his note, as observed by himself at Mentone, that is, no marked symptoms of fear, but a dislike to the spot and an effort to avoid it by going around it, or by turning back and only crossing it again after an interval of time.

"I then killed several ants on the path, using a smooth stone or a piece of ivory, instead of my finger, to crush them. In this case the ants approaching all turned back as before and with much greater exhibition of fear than when the simple finger-marks was made. This I did repeatedly. The final result was the same as obtained last winter. They persisted in coming for a week or two, during which I continued to kill them, and then they disappeared and we have seen none since. It would appear from this that while the taint of the hand is sufficient to turn them back, the killing of their fellows, with a stone or other material, produces the effects described in my first note. This was made clear to me at that time from the behaviour of the ants the first day that I killed any, for on that occasion some of them approaching the vase from below, on reaching the upper edge of the mantel, peeped over and drew back on seeing what had happened about the vase, then turned away a little and after a moment tried again at another and another point along the edge with the same result in the end. Moreover, those that found themselves among the dead and dying, went from one writhing ant to another in great haste and excitement, exhibiting the signs of fright which I described.

"I hardly hope that any will return again, but if they do, and give me an opportunity, I shall endeavour to act further on Mr. M's. suggestion.